Injection molding apparatuses, such as hot halves and hot runners, commonly use valve pins to control flow of molding material. Improper valve pin operation can cause damage to a valve pin itself or to surrounding components, such as a nozzle tip, a nozzle tip liner, a nozzle tip guide sleeve, or a mold gate. For example, on the close stroke, when a downstream tip of a valve pin is pushed into the mold gate or the area that surrounds the mold gate, the tip of the valve pin may collide with a foreign object, such as a contaminant, blocking the mold gate. Unexpectedly frozen molding material in the mold gate area can also act as a blockage. The result is that damage to the valve pin or surrounding components can occur. Similarly, a valve pin can seize before reaching the end of its close stroke, whether this be induced by material seeping between surfaces having a high-tolerance sliding relationship or by some other cause. These problems can be exasperated when several valve pins are ganged together to be actuated in unison by, for example, a common valve pin plate. In this case, the entire force transmitted by the actuator(s) to all the valve pins may be received by a single valve pin that encounters a blockage, becomes seized, or encounters some other motion inhibiting condition.
In addition, it is sometimes desired to take a valve pin out of service when a mold cavity, a valve pin, a heater, a mold gate, or other related component wears or fails. Replacement of a damaged valve pin or manual disengagement of a valve pin can be time consuming and costly.